This article explains how RBackup uses ports, with instructions on how to assign them.

All endpoints first contact the Server on its definable Command Port, usually port 2774.

The Server then tells the endpoint to call back on a different port number to send its data. Each endpoint that calls in simultaneously will be assigned a different port number called the 'Data Port,' and may attempt to use as many as five ports, depending on bandwidth availability, so the Server can handle many simultaneous endpoints quickly.

Tell the Server to assign its Data Ports in a specific range using the Web Console, Setup menu, Properties. For maximum speed under most conditions the 'Data Port Range' should have a range that includes at least 3 ports per simultaneous user, and 6 minimum. The default is 100 ports, number 29001 through 29100. (older versions used port range 1024 through 2048)

Be sure to open the same range of ports through your firewall, and forward them to the RBS Server's internal IP address through your router. If your router's DMZ is set to the RBS Server's internal IP address, there is no need to forward ports.

The software will not allow you to assign ports in a range below port 1024 to avoid conflicting with other known hardware and software that uses those ports. Otherwise, you can set the port range however you like.

Reducing the number of available ports to fewer than 3 per endpoint can result in slow transfer speeds. Changing the port range is a Server-side operation only. It is not necessary to redistribute endpoint software if you change the data port range. It is necessary to redistibute endpoint software only if you change the Command Port, which is usually 2774.